I have an 84 318i that has a miss at all speeds and the tachometer seems to bounce in unison with the miss. I have checked most of the fuel delivery pieces, good fuel pressure at all RPM's, all injectors seem to be firing OK. Just completed a complete tune up (plugs, cap, rotor, and wires). I have found the MAF meter very suspect. The resistance across pins 7 and 8 seems to float around and not give consistant numbers at any position. My plan is to replace the MAF meter, but I wanted to know if there are other items I should look at, and will the MAF cause the tach jitter I am seeing?
Not that the terminology matters much, but unless I'm wildly mistaken, the '84 318i doesn't have a MAF (mass airflow meter) unless you added one. It is an AFM (airflow meter). The MAF has a hot wire to measure resistance and electronically calculate the airflow mass. The AFM basically has a flap that moves a contact on a rheostat, but no electronics. Is there a good manual (like a Bentley) for the 318? I'm thinking that the tach is simply tracking the miss. Missing at all speeds almost eliminates a vacuum leak and, unless it persists for a few seconds at a time, I would eliminate fuel delivery problems as the cause. It is possible to clean the AFM's various parts, but I think this sounds like an ECU- or sensor-related miss. I'm not great at analyzing those, but some folks are. Look for MooseheadM5 here and maybe shoot him a PM.
I agree that the miss is likely causing the tach issue. Sounds ignition system related. Do any plugs show contamination from oil or fuel? Could be a coil or ignitor problem, could also be a faulty new component. What brand of plugs (and type) did you use? What about wires, cap and rotor?
Parts installed Thanks for all the feedback. The parts I put in were Bosch cap and rotor, and 7mm silicone aftermarket wires. The engine ran the same. The plugs are not showing any fouling, and all look the same. I do have a Haynes manual, not the caliber of the Bentley book, but I have been going through the troubleshooting items ot suggested. I feel the hesitation is more due to fuel than a miss, mainly due to a hesitation. I am changing the pickup and reluctor just cover the last of the ingnition components.
No 325ix in there either, but still Bentley is the best. I would buy the Bentley if I were you, it will pay for it's self quickly. Good luck on the problem, sorry I don't have much to offer. But do make sure all your elec connectors are clean, at this age this they are probably corroded. So clean them up. Don't forget to check ground straps too.
